1. Technical Field
The present invention relates to a printed circuit board and a manufacturing method thereof.
2. Description of the Related Art
With the trend high-density, high-integrated circuit boards, a package is mounted on a substrate largely by using a line or a pad 3 and solder ball 4 formed in a lower side of a substrate 1, as shown in FIG. 1.
The structure shown in FIG. 1, however, requires a space for a via 2 and the pad 3, respectively. Accordingly, a VOP (via on pad) structure has been suggested as shown in FIG. 2, in which a via 7 penetrating through a substrate 5 formed with a circuit pattern 6 is directly connected to a pad 8, and a solder ball 9 is coupled to the pad 8.
When the VOP structure is formed, a via hole is often formed by using a laser drill. In case of a substrate in which metal films are formed, for example, a copper clad laminate, a lower metal film is penetrated through by the laser drill.
To solve such a problem, there has been an attempt to increase the thickness of the lower metal film. However, as the lower metal film becomes thicker, it becomes more difficult to form a fine circuit.
There has been another attempt to use less energy in the laser drill. However, the laser drill with less energy has not been efficient in forming the via hole.